'Identity theft" is seen as a contemporary kind of plague and horror, the malevolent byproduct of computers and credit cards. But what really makes it so awful? It's not just the vacation you never took to Aruba. Or the embarrassing pay-per-view charges. It's the idea of being colonized by malignant forces.

Such is the subject of "The Host," a new movie based on Stephenie Meyer's first post-"Twilight" novel and a story that plays on a very primal fear. Way before Sigmund Freud theorized that multiple personalities could terrorize one psyche, "possession" was something with real consequences; people of the Middle Ages put the mentally ill to death, thinking they were possessed by demons. Certain native tribes have believed that photography could steal your soul. Jesus advised his followers to "Heal the sick, cleanse the lepers, raise the dead, cast out devils" (Matthew: 10-8).

Naturally, if there's a fear to be exploited, it's been exploited by the movies. From the multiple adaptations of "Dr. Jekyll and Mr. Hyde" to "Alien" to the multiple takes on "Invasion of the Body Snatchers" (1956, 1978 and Abel Ferrara's 1993 "Body Snatchers"), imagining evil forces moving into your head has been a popular form of entertainment. The king of possession movies -- "The Exorcist" (1973) -- is a classic, but so are many of the myriad vampire stories in which Dracula, or one of his ilk, sucks the souls out of the unfortunate, leaving them empty vessels of vascular longing.

If vampirism and alien possession are first cousins, then it wasn't a huge leap for Meyer to move into extraterrestrial-possession territory -- or to move her novel to the big screen. "The Host" (with a screenplay by director Andrew Niccol) opens Friday, starring Saoirse Ronan ("Atonement"), Diane Kruger ("Inglourious Basterds") and William Hurt. True to form, Meyer has created a supernatural hybrid, layering romantic tension on a familiar horror genre. This time, it's sci-fi.

Pod people

Which brings us back to the original "Invasion of the Body Snatchers." Although its ending was changed along with its political meaning, director Don Siegel's 1956 classic has long been viewed as that decade's quintessential Red Scare space movie, with emotionless, pre-Stepfordized creatures popping out of pods and taking over the identities of ordinary, God-fearing Americans. As Long Islander Danny Peary writes in his seminal "Cult Movies" (1981): "The pod people represent a completely regimented society. Metaphorically, they are all alike as 'two peas in a pod' because they have been sapped of their emotional individuality. The vegetarian metaphor literalizes red-scare rhetoric of the 'growth' of communism as well as the idea that revolutions are made by planting seeds."

However, the alien force behind "Invasion" had a purpose -- colonizing Earth to feed itself, before taking off to find other worlds to conquer and eat. Also, Siegel's version of identity theft was symbolic rather than literal -- the humans were replaced rather than possessed.

That was certainly not the case in 1979 and the original "Alien," in which the much-

befanged Xenomorph makes its disgusting debut, after having gestated in John Hurt's chest. This went beyond the annexation of human identity. It was the appropriation of the human body as a prenatal intergalactic petri dish. The very idea may still give readers shivers, despite the various cinematic copycat crimes committed since, including some of the official sequels.

Reasoning with an alien

The motiveless crime against humanity a la "Aliens" may be more terrifying than one in which a space race simply needs to survive, or somehow connects with human sentiment. How do you reason with an alien, a la Ridley Scott's original? You don't. And yet, with "The Host," Meyer achieves a synthesis of sorts between human emotion and ruthless invaders: A race called the Souls is taking over Earth and possessing human bodies one by one. Melanie Stryder (Ronan) has been taken over by a Soul named Wanderer but refuses to succumb. Wanderer (called Wanda) can view Melanie's memories and emotions and starts to bond with her. In the story's most curious twist, this leads to a kind of romantic quadrangle, with both Wanda and Melanie forming love bonds with two boys, played by Max Irons and Jake Abel.

With its open-ended conclusion, "The Host" is almost sure to be sequeled, as long as Meyer chooses to produce follow-ups (which she has not, as yet, done). And there's no denying she's tapped into audience appetites. In the way the "Twilight" saga married girlish dreams and ghoulish melodrama, "The Host" combines the search for the perfect someone else with the primal fear of losing oneself.

Not incidentally -- because Meyer always seems to know just what she's doing -- "The Host" also taps into ongoing debates about body image, modification and virtual reality. For many, the exploring -- and assuming -- of alternate identities is a large part of the Internet experience, and the possibilities for the horror genre already have been explored by some prescient filmmakers, such as David Cronenberg, who's been credited with the concept of "body horror" in film.

His 1999 thriller, "eXistenZ," imagined virtual-reality game players implanted with "bio-ports" through which they would connect to their game ports. Reality and its alternative soon become blurred -- something that would certainly happen if someone moved into your body. The difference between "The Host" and "eXistenZ," of course, is that one is just horrible. The other seems a lot closer to coming true.